Despite advances in percutaneous coronary intervention (PCI) for acute myocardial infarction (AMI), post ischemic microvascular obstruction (MVO) due to distal microembolization of atherothrombotic debris from the site of PCI commonly occurs and leads to failure of reperfusion. Post PCI MVO is associated with worse clinical outcomes, and effective treatments are lacking. Ultrasound (US)-induced cavitation (vibration) of intravenously injected microbubbles (MBs), offers an exciting new approach for treating MVO, which we call sonoreperfusion (SRP). While SRP has shown potential for treating venous-like thrombi in large vessels, its effects within the microvasculature, and on MVO comprised of arterial type microthrombi and atherosclerotic debris seen in AMI, are unknown. Furthermore, which US cavitational regime is most effective -- stable, inertial, or a combination thereof - is unknown. Accordingly, in this proposal, we will develop, optimize and translate SRP therapy, culminating in testing of the optimal SRP regime in perhaps the most clinically translatable large animal model of AMI and MVO available. We will first test the relative efficacies of candidate SRP platforms using an in vitro flow model of arterial MVO (Aim 1a), in which we will manipulate US variables that encompass 3 regimes: (1) stable cavitation; (2) inertial cavitation; or (3) a sequential combination of both. To understand mechanisms of action underlying successful regimes, we will study the physical consequences of MB vibrations on local fluid dynamics and tPA clot penetration (Aim 1b). In testing this mechanical hypothesis, we will be the first to use an ultra-high speed microscopy system to delve into dynamics of MB-clot interactions and the resulting physical phenomena elicited by the SRP regimes tested in Aim 1a. Insights from Aim 1b will inform further refinements in the SRP regimes --to be iteratively tested in vitro in Aim 1a- from which 3 platforms (top performer for each cavitation category) will emerge for in vivo testing in a new rat hind limb model of arterial MVO in Aim 2a. Here, in addition to efficacy, the clinical safety of each SRP platform will be assessed and factored into the final selection of a single SRP platform-that balances benefit vs. risk -- for use in Aim 3. As the in vitro model in Aim 1a precludes study of bioeffects that may mediate efficacy of a given SRP platform, we will also use the rat hind limb model to study biological effects of US-MB interactions (Aim 2b): We will test the biologic hypothesis that MB vibration-induced endothelial shear stress modulates therapeutic NO release and increased activity of endothelial derived hyperpolarizing factor. In Aim 3, we will use the best SRP regime emerging from Aim 2, in a new, clinically relevant, atherosclerotic porcine model of AMI and MVO to assess for microvascular salvage. This systematic approach will culminate in a clinically translatable SRP regime and elucidate mechanisms of action which will inform strategies for optimization of efficacy and safety.